Microsoft Calls it “by design” or a feature – most others would call it a bug. To keep things simple, if a group is added – it adds a row AND a column. In the current version (which is not accurate) when it is exported to Excel -the last row keeps getting duplicated making the Excel export NOT the same as the PDF or live report. Keep the group column is the short simple answer! It is a detail row (that is viewed in RowDetails->Advanced) that you might see NEEDS to be there for the excel export to work properly. Bug or not- this version fixes that issue.
The reference is here – the last line has Microsoft admitting that certain conditions must apply. Basicially – its a feature – here is how to fix that feature. 🙂